I. Field of the Invention
The present invention relates generally to sheet metal hemming machines.
II. Description of the Prior Art
Many manufacturing industries, e.g. the automotive industries, utilize hemming machines in order to secure two sheet metal parts together. These previously known hemming machines typically comprise a base and a nest which is vertically slidably mounted relative to the base. Hemming tooling is laterally slidably mounted to the base and movable between an extended position and a retracted position. In its extended position, the hemming tooling overlies the workpiece supported by the nest to perform the hemming operation as the nest is vertically displaced relative to the base. Conversely, in its retracted position, the hemming tooling allows the workpiece to be either loaded into or removed from the nest, as well as to move the workpiece between different sets of hemming tooling.
In order to vertically displace the nest relative to the base, it has been the previously known practice to utilize a plurality of hydraulic piston and cylinder actuators in order to vertically displace the nest in one or two stages. Still other types of hemming machines utilize at least one but preferably a plurality of electric motors to vertically displace the nest relative to the base for at least one of the two stroke stages.
A primary disadvantage of these previously known hemming machines is that the drive mechanism, i.e. the mechanism employed to vertically displace the nest relative to the base, is expensive and complex in construction. As such, they unduly increase the overall cost of the entire hemming machine.
The present invention provides a hemming machine which overcomes all of the above-mentioned disadvantages of the previously known devices.
In brief, the hemming machine of the present invention comprises a stationary base having a plate mounted to the base. A nest adapted to support a workpiece to be hemmed is vertically slidably mounted to the base above the plate.
In order to displace the nest relative to the stationary base and thus perform the hemming operation with 60 Ton to 80 Ton of force developed, an inflatable bladder is preferably sandwiched in between the plate and nest, but this bladder can also be sandwiched in between the stationary base and the plate. The bladder is selectively inflated with an incompressible fluid, such as water, and, in doing so, vertically displaces the nest relative to the plate. Consequently, upon inflation of the bladder with the incompressible fluid, the bladder compresses the workpiece against the hemming tooling thus performing the desired hemming operation.